Do you mean modulation
sources - Controller 09, 12, 13 etc.? These simply refer to generic MIDI continuous controller (CC) numbers. MIDI CC data can be generated by a MIDI controller or drawn directly in a DAW. Using the mod matrix, you can program a single controller (fader or knob or one of the Virus' "soft knobs") to affect up to 24 sound parameters.
I've never seen these controllers listed as destinations, though...
hope this helps